1. Field of the Invention
This invention generally relates to an apparatus for reproducing information from a recording medium such as an optical disc.
2. Description of the Related Art
Japanese patent application publication number 9-320200 discloses an apparatus for reproducing information from an optical disc in a 3-beam method. The apparatus of Japanese application 9-320200 applies three forward laser beams to three neighboring tracks on the optical disc, respectively. The three forward laser beams are reflected by the optical disc before returning to the apparatus. The three return laser beams are converted into three readout signals respectively. The readout signal which corresponds to central one among the three forward laser beams (or central one among the three neighboring tracks) is called the first readout signal. The other readout signals are called the second and third readout signals, respectively.
In the apparatus of Japanese application 9-320200, the first, second, and third readout signals are sampled into first, second, and third sequences of signal samples respectively. The first, second, and third sample sequences are passed through first, second, and third variable-coefficient filters to generate first, second, and third filtering-resultant sample sequences, respectively. The first filter is designed to remove signal components caused by intersymbol interferences. The second filter is designed so that the second filtering-resultant sample sequence will correspond to a crosstalk between the central track and the related track neighboring the central track. The third filter is designed so that the third filtering-resultant sample sequence will correspond to a crosstalk between the central track and the related track neighboring the central track. The second and third filtering-resultant sample sequences are subtracted from the first filtering-resultant sample sequence to generate a readout sample sequence. A final reproduced signal is derived from the readout sample sequence.
The apparatus of Japanese application 9-320200 includes a device for extracting, from the final readout sample sequence, every sample (every zero-cross sample) corresponding to a time point at which the value represented by the final readout sample sequence crosses xe2x80x9c0xe2x80x9d. The value represented by the extracted zero-cross sample is used as an error signal reflecting crosstalk-caused signal components. Filtering coefficients used by the first, second, and third filters are updated in response to the error signal so that the error signal can converge on xe2x80x9c0xe2x80x9d or crosstalk-caused components can be completely removed from the readout sample sequence. The updating of the filtering coefficients in response to the error signal is based on an LMS (least-mean-square) adaptive algorithm.
In the apparatus of Japanese application 9-320200, since only zero-cross samples are used in generating the error signal, the rate of the convergence of the error signal on xe2x80x9c0xe2x80x9d tends to be low. The apparatus of Japanese application 9-320200 does not implement partial-response waveform equalization. Therefore, the apparatus of Japanese application 9-320200 can not use a viterbi decoding process in recovering original information from a reproduced signal.
An analog signal representative of digital information which is read out from an optical disc in a tangential push-pull method has a waveform of a differential type. Also, a signal read out from a hard disk or a magnetic tape has a differential-type waveform. A differential-waveform signal takes a continuous value near xe2x80x9c0xe2x80x9d. Therefore, it is difficult for a zero-cross detection technique to sense a data change point in the differential-waveform signal. Accordingly, the apparatus of Japanese application 9-320200 can not properly operate on a differential-waveform signal.
It is an object of this invention to provide an information reproducing apparatus which can remove crosstalk-caused components from a readout signal having a differential-type waveform.
A first aspect of this invention provides an information reproducing apparatus comprising first means for reading a first signal from a first track of a recording medium; second means for reading a second signal from a second track of the recording medium, the second track neighboring the first track; a filter for filtering the second signal read by the second means into a filtering-resultant signal according to a controllable filtering characteristic; a first subtracter for subtracting the filtering-resultant signal from the first signal read by the first means to generate a subtraction-resultant signal; a peak detector for detecting whether or not a level represented by the first signal read by the first means peaks, and generating peak-point information representing a timing at which the level represented by the first signal peaks; a second subtracter for generating an error signal indicative of a difference between the subtraction-resultant signal and a prescribed reference signal at a timing equal to the timing represented by the peak-point information; and third means for controlling the filtering characteristic of the filter in response to the error signal generated by the second subtracter so as to minimize the error signal.
A second aspect of this invention provides an information reproducing apparatus comprising first means for reading a first signal of a run-length-limited code from a first track of a recording medium; second means for reading a second signal from a second track of the recording medium, the second track neighboring the first track; a transversal filter subjecting the first signal read by the first means to a partial-response waveform equalization to generate an equalization-resultant signal, the partial-response waveform equalization depending on tap coefficients; a controllable filter for filtering the second signal read by the second means into a filtering-resultant signal according to a controllable filtering characteristic; a first subtracter for subtracting the filtering-resultant signal from the equalization-resultant signal to generate a subtraction-resultant signal; third means for detecting whether or not one of (1) the first signal read by the first means and (2) the subtraction-resultant signal generated by the first subtracter corresponds to a peak point, and generating peak-point information in response to a result of said detecting; a temporary decision device for calculating a temporary decision value of the subtraction-resultant signal on the basis of a PR mode signal, an RLL mode signal, the peak-point information, and an actual value of the subtraction-resultant signal, the PR mode signal representing a type of the partial-response waveform equalization, the RLL mode signal representing a type of the run-length-limited code; a second subtracter for calculating a difference between the temporary decision value of the subtraction-resultant signal and the actual value thereof, and generating an error signal in response to the calculated difference; and fourth means for controlling the tap coefficients of the transversal filter and the filtering characteristic of the controllable filter in response to the error signal generated by the second subtracter so as to minimize the error signal.
A third aspect of this invention provides an information reproducing apparatus comprising first means for reading a first signal of a run-length-limited code from a first track of a recording medium; second means for reading a second signal from a second track of the recording medium, the second track neighboring the first track; a first A/D converter for converting the first signal read by the first means into a first digital signal; a second A/D converter for converting the second signal read by the second means into a second digital signal; third means for re-sampling the first digital signal generated by the first A/D converter to generate a first resampling-resultant signal; fourth means for generating a bit clock signal from the first digital signal generated by the first A/D converter; a first transversal filter subjecting the first re-sampling-resultant signal to a partial-response waveform equalization to generate an equalization-resultant signal, the partial-response waveform equalization depending on first tap coefficients; fifth means for re-sampling the second digital signal generated by the second A/D converter in response to the bit clock signal to generate a second re-sampling-resultant signal; a second transversal filter for filtering the second re-sampling-resultant signal into a pseudo crosstalk signal according to second tap coefficients, the pseudo crosstalk signal indicating a crosstalk between the first and second tracks; a first subtracter for subtracting the pseudo crosstalk signal from the equalization-resultant signal to generate a subtraction-resultant signal; sixth means for detecting whether or not one of (1) the first digital signal generated by the first A/D converter and (2) the subtraction-resultant signal generated by the first subtracter corresponds to a peak point, and generating peak-point information in response to a result of said detecting; a delay circuit responsive to the peak-point information generated by the fifth means for outputting at least three successive samples of the peak-point information; a temporary decision device for calculating a temporary decision value of the subtraction-resultant signal on the basis of a PR mode signal, an RLL mode signal, the successive samples of the peak-point information which are outputted from the delay circuit, and an actual value of the subtraction-resultant signal, the PR mode signal representing a type of the partial-response waveform equalization, the RLL mode signal representing a type of the run-length-limited code; a second subtracter for calculating a difference between the temporary decision value of the subtraction-resultant signal and the actual value thereof, and generating an error signal in response to the calculated difference; seventh means for controlling the first tap coefficients of the first transversal filter in response to the error signal generated by the second subtracter so as to minimize the error signal; and eighth means for controlling the second tap coefficients of the second transversal filter in response to the error signal generated by the second subtracter.
A fourth aspect of this invention is based on the third aspect thereof, and provides an information reproducing apparatus wherein at least one of the PR mode signal and the RLL mode signal remains fixed.
A fifth aspect of this invention is based on the third aspect thereof, and provides an information reproducing apparatus wherein the sixth means comprises means for detecting whether or not the subtraction-resultant signal generated by the first subtracter corresponds to a peak point, and generating peak-point information in response to a result of said detecting.
A sixth aspect of this invention is based on the second aspect thereof, and provides an information reproducing apparatus further comprising a phase-locked loop circuit for generating a system clock signal from the subtraction-resultant signal generated by the first subtracter, a delay circuit responsive to the peak-point information generated by the third means for outputting at least three successive samples of the peak-point information, and means provided in the temporary decision device for calculating the temporary decision value of the subtraction-resultant signal on the basis of the PR mode signal, the RLL mode signal, the successive samples of the peak-point information which are outputted from the delay circuit, and the actual value of the subtraction-resultant signal, wherein the third means is contained in the phase-locked loop circuit.
A seventh aspect of this invention is based on the second aspect thereof, and provides an information reproducing apparatus further comprising a phase-locked loop circuit for generating a system clock signal from the first signal read by the first means, a delay circuit responsive to the peak-point information generated by the third means for outputting at least three successive samples of the peak-point information, and means provided in the temporary decision device for calculating the temporary decision value of the subtraction-resultant signal on the basis of the PR mode signal, the RLL mode signal, the successive samples of the peak-point information which are outputted from the delay circuit, and the actual value of the subtraction-resultant signal.
An eighth aspect of this invention is based on the third aspect thereof, and provides an information reproducing apparatus wherein the type of the partial-response waveform equalization which is represented by the PR mode signal is expressed as PR (a, b, xe2x88x92b, xe2x88x92a), and the successive samples of the peak-point information are three successive samples, and wherein the temporary decision device comprises means for calculating a value P on the basis of the successive samples of the peak-point information, the value P being equal to axc2x7G when at least one of the successive samples of the peak-point information except a central sample corresponds to a peak point, the value P being equal to (a+b)xc2x7G when the central sample among the successive samples of the peak-point information corresponds to a peak point, means for detecting a polarity of a level represented by the equalization-resultant signal which occurs when the central sample among the successive samples of the peak-point information corresponds to a peak point, means for calculating the temporary decision value on the basis of the calculated value P and the detected polarity, and means for setting the temporary decision value to xe2x80x9c0xe2x80x9d when none of the successive samples of the peak-point information corresponds to a peak point, where G denotes a gain factor.
A ninth aspect of this invention is based on the third aspect thereof, and provides an information reproducing apparatus wherein the type of the partial-response waveform equalization which is represented by the PR mode signal is expressed as PR (a, b, xe2x88x92b, xe2x88x92a), and the successive samples of the peak-point information are five successive samples, and wherein the temporary decision device comprises means for calculating a value P on the basis of the successive samples of the peak-point information, the value P being equal to axc2x7G when at least one of second and fourth samples among the successive samples of the peak-point information corresponds to a peak point, the value P being equal to (a+b)xc2x7G when the central sample among the successive samples of the peak-point information corresponds to a peak point, means for detecting a polarity of a level represented by the equalization-resultant signal which occurs when the central sample among the successive samples of the peak-point information corresponds to a peak point, means for calculating the temporary decision value on the basis of the calculated value P and the detected polarity, and means for setting the temporary decision value to xe2x80x9c0xe2x80x9d when none of second, third, and fourth samples among the successive samples of the peak-point information corresponds to a peak point, where G denotes a gain factor.
A tenth aspect of this invention is based on the first aspect thereof, and provides an information reproducing apparatus wherein the first means comprises means for reading the first signal from the first track of the recording medium in a tangential push-pull method.
An eleventh aspect of this invention provides an information reproducing apparatus comprising first means for reading a first signal from a first track of a recording medium; second means for reading a second signal from a second track of the recording medium, the second track neighboring the first track; a filter for filtering the second signal read by the second means into a filtering-resultant signal according to a controllable filtering characteristic; a first subtracter for subtracting the filtering-resultant signal from the first signal read by the first means to generate a subtraction-resultant signal; a zero-cross detector for detecting whether or not a level represented by the first signal read by the first means crosses zero, and generating 0-point information representing a timing at which the level represented by the first signal crosses zero; a peak detector for detecting whether or not the level represented by the first signal read by the first means peaks, and generating peak-point information representing a timing at which the level represented by the first signal peaks; third means for selecting one of (1) the 0-point information generated by the zero-cross detector and (2) the peak-point information generated by the peak detector; a second subtracter for generating an error signal indicative of a difference between the subtraction-resultant signal and a prescribed reference signal at a timing equal to the timing represented by the information selected by the third means; and fourth means for controlling the filtering characteristic of the filter in response to the error signal generated by the second subtracter so as to minimize the error signal.
A twelfth aspect of this invention provides an information reproducing apparatus comprising first means for reading a first signal of a run-length-limited code from a first track of a recording medium; second means for reading a second signal from a second track of the recording medium, the second track neighboring the first track; a transversal filter subjecting the first signal read by the first means to a partial-response waveform equalization to generate an equalization-resultant signal, the partial-response waveform equalization depending on tap coefficients; a controllable filter for filtering the second signal read by the second means into a filtering-resultant signal according to a controllable filtering characteristic; a first subtracter for subtracting the filtering-resultant signal from the equalization-resultant signal to generate a subtraction-resultant signal; third means for detecting whether or not one of (1) the first signal read by the first means and (2) the subtraction-resultant signal generated by the first subtracter corresponds to a zero-cross point, and generating 0-point information in response to a result of said detecting; fourth means for detecting whether or not one of (1) the first signal read by the first means and (2) the subtraction-resultant signal generated by the first subtracter corresponds to a peak point, and generating peak-point information in response to a result of said detecting; fifth means for selecting one of (1) the 0-point information generated by the third means and (2) the peak-point information generated by the fourth means; a temporary decision device for calculating a temporary decision value of the subtraction-resultant signal on the basis of a PR mode signal, an RLL mode signal, the information selected by the fifth means, and an actual value of the subtraction-resultant signal, the PR mode signal representing a type of the partial-response waveform equalization, the RLL mode signal representing a type of the run-length-limited code; a second subtracter for calculating a difference between the temporary decision value of the subtraction-resultant signal and the actual value thereof, and generating an error signal in response to the calculated difference; and sixth means for controlling the tap coefficients of the transversal filter and the filtering characteristic of the controllable filter in response to the error signal generated by the second subtracter so as to minimize the error signal.
A thirteenth aspect of this invention provides an information reproducing apparatus comprising first means for reading a first signal of a run-length-limited code from a first track of a recording medium; second means for reading a second signal from a second track of the recording medium, the second track neighboring the first track; a first A/D converter for converting the first signal read by the first means into a first digital signal; a second A/D converter for converting the second signal read by the second means into a second digital signal; third means for re-sampling the first digital signal generated by the first A/D converter to generate a first re-sampling-resultant signal; fourth means for generating a bit clock signal from the first digital signal generated by the first A/D converter; a first transversal filter subjecting the first re-sampling-resultant signal to a partial-response waveform equalization to generate an equalization-resultant signal, the partial-response waveform equalization depending on first tap coefficients; fifth means for re-sampling the second digital signal generated by the second A/D converter in response to the bit clock signal to generate a second re-sampling-resultant signal; a second transversal filter for filtering the second re-sampling-resultant signal into a pseudo crosstalk signal according to second tap coefficients, the pseudo crosstalk signal indicating a crosstalk between the first and second tracks; a first subtracter for subtracting the pseudo crosstalk signal from the equalization-resultant signal to generate a subtraction-resultant signal; sixth means for detecting whether or not one of (1) the first digital signal generated by the first A/D converter and (2) the subtraction-resultant signal generated by the first subtracter corresponds to a zero-cross point, and generating 0-point information in response to a result of said detecting; seventh means for detecting whether or not one of (1) the first digital signal generated by the first A/D converter and (2) the subtraction-resultant signal generated by the first subtracter corresponds to a peak point, and generating peak-point information in response to a result of said detecting; eighth means for selecting one of (1) the 0-point information generated by the sixth means and the peak-point information generated by the seventh means; a delay circuit responsive to the information selected by the eighth means for outputting at least three successive samples of the information selected by the eighth means; a temporary decision device for calculating a temporary decision value of the subtraction-resultant signal on the basis of a PR mode signal, an RLL mode signal, the successive samples of the information which are outputted from the delay circuit, and an actual value of the subtraction-resultant signal, the PR mode signal representing a type of the partial-response waveform equalization, the RLL mode signal representing a type of the run-length-limited code; a second subtracter for calculating a difference between the temporary decision value of the subtraction-resultant signal and the actual value thereof, and generating an error signal in response to the calculated difference; ninth means for controlling the first tap coefficients of the first transversal filter in response to the error signal generated by the second subtracter so as to minimize the error signal; and tenth means for controlling the second tap coefficients of the second transversal filter in response to the error signal generated by the second subtracter.
A fourteenth aspect of this invention is based on the thirteenth aspect thereof, and provides an information reproducing apparatus wherein at least one of the PR mode signal and the RLL mode signal remains fixed.
A fifteenth aspect of this invention is based on the thirteenth aspect thereof, and provides an information reproducing apparatus wherein the sixth means comprises means for detecting whether or not the subtraction-resultant signal generated by the first subtracter corresponds to a zero-cross point, and generating 0-point information in response to a result of said detecting, and the seventh means comprises means for detecting whether or not the subtraction-resultant signal generated by the first subtracter corresponds to a peak point, and generating peak-point information in response to a result of said detecting.
A sixteenth aspect of this invention is based on the twelfth aspect thereof, and provides an information reproducing apparatus further comprising a phase-locked loop circuit for generating a system clock signal from the subtraction-resultant signal generated by the first subtracter, a delay circuit responsive to the information selected by the fifth means for outputting at least three successive samples of the information selected by the fifth means, and means provided in the temporary decision device for calculating the temporary decision value of the subtraction-resultant signal on the basis of the PR mode signal, the RLL mode signal, the successive samples of the information which are outputted from the delay circuit, and the actual value of the subtraction-resultant signal, wherein the third means and the fourth means are contained in the phase-locked loop circuit.
A seventeenth aspect of this invention is based on the twelfth aspect thereof, and provides an information reproducing apparatus further comprising a phase-locked loop circuit for generating a system clock signal from the first signal read by the first means, a delay circuit responsive to the information selected by the fifth means for outputting at least three successive samples of the information selected by the fifth means, and means provided in the temporary decision device for calculating the temporary decision value of the subtraction-resultant signal on the basis of the PR mode signal, the RLL mode signal, the successive samples of the information which are outputted from the delay circuit, and the actual value of the subtraction-resultant signal.
An eighteenth aspect of this invention is based on the twelfth aspect thereof, and provides an information reproducing apparatus further comprising seventh means for changing the partial-response waveform equalization by the transversal filter between PR (a, b, b, a) equalization and PR (a, b, xe2x88x92b, xe2x88x92a) equalization.
A nineteenth aspect of this invention is based on the eleventh aspect thereof, and provides an information reproducing apparatus wherein the first means comprises means for reading the first signal from the first track of the recording medium in a tangential push-pull method.
A twentieth aspect of this invention provides an information reproducing apparatus comprising first means for reading a first signal from a first track of a recording medium; second means for reading a second signal from a second track of the recording medium, the second track neighboring the first track; a filter for filtering the second signal read by the second means into a filtering-resultant signal according to a controllable filtering characteristic; a first subtracter for subtracting the filtering-resultant signal from the first signal read by the first means to generate a subtraction-resultant signal; a peak detector for detecting whether or not a level represented by the first signal read by the first means peaks, and generating peak-point information representing a timing at which the level represented by the first signal peaks; a temporary decision circuit for implementing a temporary decision about the subtraction-resultant signal generated by the first subtracter, and generating a temporary decision result signal representing a result of the temporary decision; a second subtracter for generating an error signal indicative of a difference between the subtraction-resultant signal and the temporary decision result signal at a timing equal to the timing represented by the peak-point information; and third means for controlling the filtering characteristic of the filter in response to the error signal generated by the second subtracter so as to minimize the error signal.
A twenty-first aspect of this invention provides an information reproducing apparatus comprising first means for reading a first signal from a first track of a recording medium; second means for reading a second signal from a second track of the recording medium, the second track neighboring the first track; a filter for filtering the second signal read by the second means into a filtering-resultant signal according to a controllable filtering characteristic; a first subtracter for subtracting the filtering-resultant signal from the first signal read by the first means to generate a subtraction-resultant signal; a zero-cross detector for detecting whether or not a level represented by the first signal read by the first means crosses zero, and generating 0-point information representing a timing at which the level represented by the first signal crosses zero; a peak detector for detecting whether or not the level represented by the first signal read by the first means peaks, and generating peak-point information representing a timing at which the level represented by the first signal peaks; third means for selecting one of (1) the 0-point information generated by the zero-cross detector and (2) the peak-point information generated by the peak detector; a temporary decision circuit for implementing a temporary decision about the subtraction-resultant signal generated by the first subtracter, and generating a temporary decision result signal representing a result of the temporary decision; a second subtracter for generating an error signal indicative of a difference between the subtraction-resultant signal and the temporary decision result signal at a timing equal to the timing represented by the information selected by the third means; and fourth means for controlling the filtering characteristic of the filter in response to the error signal generated by the second subtracter so as to minimize the error signal.